This invention relates generally to means for packaging printed circuit boards into a functional piece of electronic equipment and more particularly the invention relates to an arrangement of printed circuit board retaining modules which are stackable, one upon the other, with two or more power bus bars extending through the stack of modular card retaining modules to secure said modules together and also to supply two or more power supplies to the printed circuit cards inserted in the individual retaining modules.
In the present state of the art printed circuit boards are commonly retained in card cages. Such card cages function generally to receive printed circuit cards in slots formed in the card cage in such a manner that the cards are stacked one upon the other and spaced apart predetermined distances. Interconnections between the cards are commonly made by a back panel which can have a plurality of card edge connectors secured thereon, each of which receives one of the printed circuit boards. The interconnections between the printed circuit boards are commonly made by point-to-point wiring between terminal posts which extend through the back panel and into the card edge connectors where they make contact with circuit pads on the edge of the printed circuit boards.
Various power supplies are required for most systems and can consist of two or more different DC voltages which are supplied to the printed circuit boards by separate power supply voltage carrying conductors which are connected to appropriate terminals on the back panel.
Other known means of supplying power to the printed circuit boards include multi-layer back panels in which one of the conductive levels has sufficient current carrying capacity to feed the various circuit boards. Such electric current, however, can amount to several hundred amperes in the case of fairly complex electronic systems which might utilize several tens of printed circuit boards, with a large number of integrated circuit chips mounted on each circuit board. Each printed circuit board could, for example, easily require twenty-five to thirty amperes.
The problems of supplying power to the circuit boards by means of separate conductors lie largely in the relatively large number of conductors required. The problems of supplying power to the various circuit boards by means of conductive levels in the back panel lie primarily in the heat dissipation problems involved in conducting such a large number of amperes in the relatively constrained conductive levels on the back panel.
A further problem in the use of multi-level printed circuit boards for the purpose of supplying power to the printed circuit boards lies in the difficulty of connecting both the power supplying leads and the signal supplying leads to the edge of the printed circuit board from the common back panel system.